Chemical mechanical planarization, also called chemical mechanical polishing (and commonly abbreviated CMP), includes processes that are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, oxide layers, conductive layers, and layers of metal or glass, and the like. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
A conventional CMP process involves pressing a substrate (e.g. a wafer substrate) against a rotating polishing pad in the presence of a polishing compound (also referred to as a polishing slurry). The polishing pad is held on a platen in the CMP apparatus whereas the substrate wafer being polished is held above the polishing pad with a dynamic polishing head. The dynamic polishing head holding the wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The polishing slurry generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing slurry typically contains one or more chemicals that interact with or dissolve portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). This action removes material from the substrate and tends to even out irregular topography on the substrate, making the substrate surface flat or planar. For example, such CMP operations may be used to either bring the entire substrate surface within the depth of focus for a following photolithography operation, or to selectively remove material based on its position on the substrate.
In general, there is a need to detect when the desired surface planarity or layer thickness has been reached or when an underlying layer has been exposed in order to determine whether to stop polishing. Several techniques have been developed for the in situ detection of endpoints during the CMP process. For example, an optical monitoring system for in-situ measuring of uniformity of a layer on a substrate during polishing of the layer has been employed. The optical monitoring system can include a light source that directs a light beam toward the substrate during polishing, a detector that measures light reflected from the substrate, and a computer that analyzes a signal from the detector and calculates whether the endpoint has been detected. In some CMP systems, the light beam is directed toward the substrate through the local area transparency in the polishing pad.
Such polishing pads having local area transparencies are known in the art and have been used to polish work pieces, such as semiconductor devices. For example, U.S. Pat. No. 5,893,796 discloses removing a portion of a polishing pad to provide an aperture and placing a transparent two-section top hat design polyurethane or quartz plug in the aperture to provide the local area transparency. Typically, local area transparencies are mounted into the top polishing pad layer and are either flush with the top polishing surface of the polishing pad or are recessed from the polishing surface. Local area transparencies that are mounted flush can become scratched and clouded during polishing and/or during conditioning resulting in polishing defects and hindering endpoint detection. Accordingly, it is desirable to recess the local area transparency from the plane of the polishing surface to avoid scratching or otherwise damaging the LAT. Polishing pads having recessed local area transparencies are disclosed in U.S. Pat. Nos. 5,433,651, 6,146,242, 6,254,459, 6,280,290, and 7,195,539 as well as U.S. Published Patent Application Nos. 2002/0042243 A1 and 2003/0171081 A1.
Conventional methods for affixing a LAT into a polishing pad typically involve either the use of an adhesive to attach the local area transparency to the pad, or an integral molding method. Such conventional methods produce polishing pads which may suffer one or both of the following problems: (1) the seal between the polishing pad and the local area transparency is either imperfect or deteriorates during use such that polishing slurry leaks through this imperfection and onto the platen or behind the local area transparency thus compromising optical clarity for endpoint detection, and (2) the local area transparency may separate from the polishing pad during use and be ejected because the slurry may compromise the adhesive interface.
Thus, there remains a need for an effective polishing pad comprising a translucent region (e.g., local area transparency) that avoids wear by the workpiece because it is recessed and can be produced using efficient and inexpensive methods. The present invention provides such a polishing pad, as well as methods of making such pads. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.